Abstract ID: 192

Climatic Consequences of Gradual Conversion of Amazonian Tropical Forests Into Degraded Pasture or Soybean Cropland: a new Vegetation-Climate Equilibrium State in Amazonia

This study evaluates the climatic consequences caused by gradual change of Amazonian tropical forests into degraded pasture or soybean cropland. To that end, we used the CPTEC-INPE AGCM and the CPTEC-INPE Potential Vegetation Model (PVM). The study is divided in two parts: (I) the numerical simulations kept the biomes unchanged throughout the integration and did not interact with climate (II) the biomes were allowed to interact with climate freely, therefore they can change during the integration. In part I, we employed the CPTEC-INPE AGCM to assess the effects of Amazonian deforestation on the regional and global climate, using two ways to assign land cover: 1) land cover projections of deforestation and replacement by degraded pasture or soybean cropland from a business-as-usual scenario of future deforestation and 2) land cover projections from random scenarios of deforestation and replacement by degraded pasture. The results show that changes in vegetation cover in Amazonia modified the calculated fields of radiation, energy, water balance, and the dynamical structure of the atmosphere, and consequently the moisture and mass convergence in low levels of the atmosphere, mainly in dry season. The main impacts on Amazonia climate, because of deforestation, occur over eastern and central Amazonia, and are more evident when total deforested area is larger than 40%. The results for eastern Amazonia, where changes in land cover are expected to be larger during this century, show increase in near-surface air temperature, and decrease in evapotranspiration and precipitation, which occurs mainly during the dry season. The relationship between precipitation and deforestation shows higher rate of decrease of rainfall for increasing deforestation for both classes of land use conversions and all scenarios. In part II, the CPTEC-PVM was asynchronously coupled to the CPTEC AGCM. We found two biosphere-atmosphere equilibrium states for South America as in Oyama and Nobre (2003): 1) present-day potential biomes 2) a new vegetation-climate equilibrium where the eastern part of the Amazonia tropical forest are replaced by tropical savannas, and semi-desert and desert areas appear in Northeast of Brazil. In this study we found that the threshold of 50% of total deforested area in Amazonia is the threshold for transition from present-day potential biomes to a new vegetation-climate equilibrium state in Amazonia.

Session:  Feedbacks to Climate - Effects of deforestation on regional and global climate.

Presentation Type:  Oral